Let us assume that you have played a few games of Othello, and that you have decided that you like to have discs in the corners, since they can never be taken from you. In this case you have probably decided that you prefer not to play next to empty corners (you don't want your opponent to get the corners instead of you), and so you try to avoid playing on X-squares and C-squares (see the Notation section). When you are playing beginners who have not yet realised that corners are important, you may well win easily just by waiting for them to give you the corners. But if your opponent is also trying to avoid playing next to corners, you will need a new plan!
..###O.. ..O###.. OOO###.. O#####.. O##OO#.. OO####.. ..OO##.. ..OOO...
White to play;:
Look at the position in the diagram above. You are White, and it's your move. So far everything is going to plan: you have kept away from the C-squares and X-squares. Unfortunately so has your opponent, and you are a bit worried because he has more discs than you. Suddenly, you spot a really huge move at f8, turning 10 discs at once. You play it and arrive at the middle position above. Surely your opponent can not recover from this? But to your amazement, your opponent plays to g1, a C-square! Strangely enough, you can not see any way to exploit this dangerous looking move. In fact you now realise to your horror that your only moves are to the awful X-squares at b7 and g2, either of which will immediately give your opponent a corner. Disaster! So what has gone wrong?
Let's look again at the initial position. At the moment you have a lot of choices. Why have you got so much choice? Because your opponent has a lot of discs available to be flipped. Almost all your choices disappeared when you greedily turned all those discs over by playing f8. So perhaps something less greedy would be better?
..###O.. ..O###.. OOO###.. O#####.. O##OO#.. OO####.. ..OO##.. ..OOO...
Original position;:
If you look more closely at the original position, you will see that it is in fact Black who has very few safe moves at the moment. In fact, g1 is the only move which does not give away a corner immediately. You can stop Black from playing g1 if you wish by playing b1. Is this a good idea? After all it is a C-square! But, as shown above, after you play b1, Black has no safe moves at all. Whatever Black does next, you will be able to take a corner immediately.
What is the moral? Well, don't be too greedy in the middle of the game: save your greed until it is needed at the end! Also, it is a good idea to keep track of where your available moves are, and where the opponent's are. That way you can avoid disasters like the one above when you tried f8. Of course, if neither of you takes too many pieces, then you will need a new plan ...